1. Field of the Invention
The invention relates to a method for operating an internal combustion engine, in particular a gas engine, having at least three cylinders, wherein a cylinder-specific signal is acquired from each cylinder, wherein a reference value is generated from the signals from the cylinders, wherein at least one combustion parameter of the corresponding cylinder is controlled as a function of the deviation of a signal from the reference value, whereupon the signal tracks the reference value.
2. Description of Related Art
The cylinders of an internal combustion engine normally exhibit technical differences in combustion, i.e. when combustion parameters such as the quantity of fuel or the ignition point are controlled in an overall manner, the individual contributions by the cylinders to the total work carried out by the internal combustion engine are different. The term “overall control” or “overall engine control” of combustion parameters as used in the context of the invention means that all of the cylinders of an internal combustion engine are operated with the same values for the corresponding variables, i.e., for example, for overall control as regards fuel quantity, the same open period is applied to the gas injection valves for the cylinders, or for overall control as regards the ignition point, the ignition devices of the cylinders are each activated at the same piston position of the respective piston in the cylinder—normally expressed as the crank angle before TDC (top dead center of the piston in the cylinder).
The work of a cylinder in a reciprocating engine is transmitted via a crankshaft connected to a connecting rod of the cylinder to an output shaft of the internal combustion engine, wherein frequently, an electrical generator is connected to the output shaft in order to convert the mechanical energy of the output shaft into electrical energy. Of the various possibilities for cylinder balancing, focus is on balancing the peak pressures in the individual cylinders in order to obtain as even as possible a mechanical peak load on the components. Examples of major alternative balancing variations are optimizing the engine efficiency or minimizing pollutant emissions.
Having regard to cylinder balancing control, U.S. Pat. No. 7,957,889 B2 describes tailoring the introduction of fuel for each cylinder of an internal combustion engine such that the maximum internal cylinder pressure or peak cylinder pressure of each cylinder is set to a common target value with a tolerance band. The target value in that case is obtained from the arithmetic mean of all of the peak cylinder pressures.
By balancing the peak cylinder pressures, each cylinder provides essentially the same contribution to power and thermo-mechanical overloading of individual cylinders can be avoided. Furthermore, fuel metering can give rise to knocking combustion. Thus, it can, for example, be provided that cylinders which exceed a certain knocking intensity do not receive an increased fuel supply in order to avoid more severe knocking and possible mechanical damage.
The systems described until now use the arithmetic mean of cylinder-specific signals such as the peak cylinder pressure as the target variable for cylinder balance control. However, using the arithmetic mean suffers from the disadvantage that large rogue results have a major impact on the arithmetic mean. Thus, for example, cylinders which exhibit poor combustion or for which the cylinder pressure signal is imprecise or wrong—for example due to a defective sensor or aging of the sensors or electromagnetic interference in the signal transmission and/or signal processing—have a significant and above all unwelcome influence on the target value for all peak cylinder pressures.